Maria Grazia Musolino

Particle size effect in the catalytic hydrogenation of 2,4-dinitrotoluene over Pd/C catalysts

Abstract The liquid phase hydrogenation of 2,4-dinitrotoluene (2,4-DNT) to 2,4-diaminotoluene (2,4-DAT) has been studied over palladium supported on carbon. Catalytic activity and selectivity to the intermediate products were found to depend on the metal particle size. The larger metal particles were the most active and selective towards the formation of the 2,4-nitrohydroxyaminotoluene isomers. The catalysts have been characterized by TPR, XRD, TEM and CO chemisorption. TPR analysis has shown that no formation of a palladium β-hydride phase occurs on these systems irrespectively of the metal particle size. This apparently anomalous behavior has been attributed to the contamination of the Pd metal particles by impurities and/or C atoms migrating from the support. On the basis of the reported results the relationships between the catalytic activity and the metal particle size in the hydrogenation of 2,4-DNT is discussed.

Catalytic combustion of diesel soot over metal oxide catalysts

Abstract The activity of different metal oxides in the catalytic combustion of a diesel soot having a high amount of adsorbed hydrocarbons has been investigated and tested in a TPO apparatus. Two different steps have been observed. The first is related to the combustion of hydrocarbons adsorbed on soot and the second one to the combustion of the graphitic solid fraction. A high surface area Fe2O3 was found to be the most active catalyst for the oxidation of hydrocarbons, whereas V2O5 was also able to promote the combustion of graphitic carbon. The oxidation of the hydrocarbon fraction has been correlated with the surface area and the strength of the metal-oxygen bond of the metal oxide. The combustion of graphitic carbon is favoured instead on metal oxides having a low melting point. The effect of platinum addition to γ-alumina has been also investigated. Spillover of activated oxygen from Pt to the support has been postulated to take into account the promotion of the oxidation of graphitic carbon.

Selective transfer hydrogenolysis of glycerol promoted by palladium catalysts in absence of hydrogen

Selective conversion of glycerol into 1,2-propanediol in the presence of a Pd/Fe2O3catalyst, under inert atmosphere, is reported for the first time; the hydrogen necessary for the hydrogenolysis reaction derives from the dehydrogenation of the solvent (2-propanol or ethanol), promoted by supported palladium, itself reduced “in situ” by alcohols.

Glycerol hydrogenolysis promoted by supported palladium catalysts.

Catalytic hydrogenolysis, with high conversion and selectivity, promoted by supported palladium substrates in isopropanol and dioxane at a low H(2) pressure (0.5 MPa), is reported for the first time. The catalysts, characterized by using BET isotherms, transmission electron microscopy (TEM), temperature-programmed reduction (TPR), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were obtained by coprecipitation and impregnation techniques. The coprecipitation method allows catalysts with a metal-metal or a metal-support interaction to be obtained, which enhances the catalytic performance for both the conversion of glycerol and the selectivity to 1,2-propanediol. Analogous reactions carried out with catalysts prepared by using impregnation are less efficient. A study of the solvent and temperature effect is also presented. The obtained results allow the hydrogenolysis mechanism to be inferred; this involves both the direct replacement of the carbon-bonded OH group by an incoming hydrogen or the formation of hydroxyacetone as an intermediate, which subsequently undergoes a hydrogenation process to give 1,2-propanediol. Finally, catalytic tests on a large-scale reaction at a higher H(2) pressure and recycling of the samples were carried out with the better performing catalysts (Pd/CoO and Pd/Fe(2)O(3) prepared by using coprecipitation) to verify possible industrial achievements.

K- and Cs-FeV/Al2O3 soot combustion catalysts for diesel exhaust treatment

Abstract Alkali-doped FeV oxide catalysts supported on α-alumina were prepared and their catalytic activity in the combustion of diesel soot is reported. The catalysts were characterized by XRD, TPR and SEM–EDX analysis. The influence of the nature of the alkali metal (K and Cs), the temperature of treatment of the catalysts and the stability to sulfur poisoning have been investigated. Catalysts doped with Cs were the most active and stable also after several combustion cycles and in the presence of sulfur in the stream. The activity measurements and microstructural results suggest that the combustion of soot is favored on catalysts where amorphous phases and/or mixed FeVO phases, ensuring an intimate contact between iron and vanadium, are present. A reaction mechanism involving the participation of the redox couple Fe(II)–Fe(III) in the activation of the vanadium combustion sites, is proposed.

Thermal analysis characterization of promoted vanadium oxide-based catalysts

Abstract Vanadium oxide-based catalysts promoted with KCl and a transition metal chloride (M=Cu, Ce, Fe, Co, Zn) have been investigated in the oxidation of diesel soot and characterized by thermal analysis techniques, such as temperature-programmed reduction (TPR) and differential scanning calorimetry (DSC). Aim of the study was to acquire information on the reaction mechanism of the catalytic soot combustion over these catalytic systems. Data presented suggest that the activity of investigated catalysts is correlated to their reducibility which favor the redox activity of the active vanadium species. The formation of eutectics between components of the catalyst also occur improving the catalyst–carbon contact.

Mechanism of 2,4-dinitrotoluene hydrogenation over Pd/C

Abstract Hydrogenation of 2,4-dinitrotoluene (DNT) to 2,4-diaminotoluene (DAT) has been carried out over a 5% Pd/C catalyst. Gas chromatography and liquid chromatography have been used to detect the reaction intermediates. 4-Hydroxylamine,2-nitrotoluene (4HA2NT) is the main reaction intermediate. The two amino-nitro compounds 4-amino,2-nitrotoluene (4A2NT) and 2-amino,4-nitrotoluene (2A4NT) are the other relevant intermediates found. 4HA2NT decomposes by exposure to air and in the GC injector thus complicating the analysis of the reaction mixture. A simple procedure has been developed to perform the GC analysis without interference of the hydroxylamine. A kinetic study has been also carried out and a reaction pathway has been proposed. Intermediates are formed from DNT through three parallel reactions. They are then hydrogenated to the final product DAT by a series of consecutive reactions.

Liquid Phase Hydrogenation of 2-Butyne-1,4-Diol and 2-Butene-1,4-Diol Isomers over Pd Catalysts. Roles of Solvent, Support and Proton on Activity and Products Distribution

Hydrogenation of 2-butyne-1,4-diol has been investigated over palladium supported catalysts. It was found that, besides butane-1,4-diol, side products such as cis- and trans-2-butene-1,4-diol, 2-hydroxytetrahydrofuran, cis- and trans-crotyl alcohol and n-butanol were also formed. The hydrogenation of the intermediates cis- and trans-2-butene-1,4-diol has been investigated too. On the basis of the results reported, a reaction scheme for the hydrogenation of 2-butyne-1,4-diol is proposed. The influence of proton, nature of solvent and carbon support on activity and products distribution has been studied in the hydrogenation of cis-2-butene-1,4-diol. The use of water as solvent shows a better activity and selectivity to butane-1,4-diol and suppresses the hydrogenolysis reaction more than other solvents used. Addition of proton leads to a major formation of hydrogenolysis and isomerisation products. A higher activity and selectivity to isomerisation products were obtained on the palladium catalysts supported on acid modified carbon.

Hydrogenolysis vs. aqueous phase reforming (APR) of glycerol promoted by a heterogeneous Pd/Fe catalyst

The hydrogenolysis and the aqueous phase reforming of glycerol have been investigated under mild reaction conditions, using water as the reaction medium and Pd/Fe as the catalyst. The experiments, in the presence of added H2 or under inert atmosphere, clearly show that the dehydration/hydrogenation route is the key step in the case of C–O bond cleavage (hydrogenolysis) while dehydrogenation is a prerequisite for C–C bond breaking (APR), with the latter favoured at higher reaction temperatures. The temperature dependence of the C–C and C–O bond rupture is discussed by taking into account the bond energies involved in the competitive hydrogenolysis and APR reactions. Finally, the Pd/Fe catalyst was also tested in the hydrogenolysis and APR of ethylene glycol in the same temperature range, with the aim of clarifying the selective cleavage of C–O and C–C bonds in biomass derived C2–C3 polyols.

Catalytic hydrogenation of 2,4-dinitrotoluene over a Pd/C catalyst : identification of 2-(Hydroxyamino)-4-nitrotoluene (2HA4NT) as reaction intermediate

The catalytic hydrogenation of 2,4-DNT over palladium supported on carbon catalysts is reported. The 2-(hydroxyamino)-4-nitrotoluene (2HA4NT) was identified as a reaction intermediate. The characterization of this compound and the reasons for its formation are discussed.